Preceramic metallopolysilanes

ABSTRACT

A process for the preparation of preceramic metallopolysilanes is described. The process consists of reacting polysilanes with metallic compounds from which can be generated open coordination sites associated with the metallic element. Such open coordination sites can be generated by the reduction of the metallic compound with an alkali metal reducing agent, or by heating a metallic compound which has thermally labile ligands, or by the UV irradiation of a carbonyl-containing metallic compound. The metals which can be incorporated into the polysilane include aluminum, boron, chromium, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium, niobium, and tantalum. These metallopolysilanes are useful, when fired at high temperatures, to form metal-containing ceramic materials.

BACKGROUND OF INVENTION

This invention relates to the preparation of metallopolysilanes. Morespecifically, this invention relates to the preparation ofmetallopolysilanes which contain significant amounts of aluminum, boron,chromium, molybdenum, tungsten, titanium, zirconium, hafnium, vanadium,niobium, or tantalum. These polymers are useful as chemicalintermediates to synthesize other metal-containing organosiliconmaterials or polymers. These polymers can also be converted, when firedat high temperatures, to ceramic materials.

What is disclosed herein is a novel process to obtain metallopolysilanesby reacting polysilanes with certain metal-containing compounds orcomplexes. The metals are oxidatively added to the polysilane.Polysilanes with significantly higher metallic levels, relative to othermethods of incorporating the metal components, can be prepared by theprocesses of this invention.

Chandra et al. in U.S. Pat. No. 4,762,895 described a method ofpreparing metallopolysilanes by reacting organohalogendisilanes withmetal-containing compounds (such as metal halides) in the presence of aredistribution catalyst in an inert, essentially anhydrous atmosphereand removing volatile byproducts. The metal components were incorporatedinto the polysilane during the actual formation of the polysilane. Thehighest level of metal incorporation reported was about five weightpercent; generally, the reported metal content of the metal-containingpolysilanes was less than about two weight percent.

In Japanese Kokai Tokyo Koho Nos. 58/213023 and 59/161430 titanium- orzirconium-containing preceramic polymers were prepared by reactingpolysilanes with titanium alkoxides or zirconium alkoxides. Suchmaterials are expected to contain [Ti-O] and [Zr-O] units.

What is newly discovered is that metallopolysilanes can be prepared byreacting polysilanes with certain metallic compounds under conditionswhere open or unoccupied coordination sites can be generated.

THE INVENTION

This invention relates to a method of preparing a metallopolysilane,which method comprises (A) contacting a polysilane with a metalliccompound capable of generating open coordination sites where themetallic compound contains a metal selected from the group consisting ofaluminum, boron, chromium, molybdenum, tungsten, titanium, zirconium,hafnium, vanadium, niobium, and tantalum and (B) forming opencoordination sites of the metallic compound, in the presence of thepolysilane, until a metallopolysilane is obtained.

This invention also relates to a method for preparing a ceramic materialwhich method consists of heating a metallopolysilane in an inertatmosphere or in a vacuum to a temperature of at least 750° C. until themetallopolysilane is converted to a ceramic material, where themetallopolysilane is prepared by a method which comprises (A) contactinga polysilane with a metallic compound capable of generating opencoordination sites where the metallic compound contains a metal selectedfrom the group consisting of aluminum, boron, chromium, molybdenum,tungsten, titanium, zirconium, hafnium, vanadium, niobium, and tantalumand (B) forming open coordination sites of the metallic compound, in thepresence of the polysilane, until a metallopolysilane is obtained.

This invention concerns the preparation of metallopolysilanes byreacting polysilanes with certain metallic compounds or complexes. Thepolysilanes useful in this invention are characterized by Si-Si bonds inthe skeletal backbone. The polysilanes should be capable of beingconverted to a ceramic material by pyrolysis to elevated temperatures.Preferably the polysilane should be capable of being converted to aceramic product in a 20% or more yield; more preferably the ceramicyield of the polysilane should be greater than about 40%. Suchpolysilanes are well known in the art. The polysilane may contain unitsof general structure [R₃ Si], [R₂ Si], and [RSi] where each R isindependently selected from the group consisting of hydrogen, alkylradicals containing 1 to 20 carbon atoms, phenyl radicals, vinylradicals, and radicals of the formula A_(y) X'.sub.(3-y) Si(CH₂)_(z) --where A is a hydrogen atom or an alkyl radical containing 1 to 4 carbonatoms, y is an integer equal to 0 to 3, X' is chlorine or bromine, and zis an integer greater than or equal to 1. Polysilanes useful in thisinvention may contain silane units such as [Me₂ Si], [MeSi], [PhMeSi],[PhSi], [ViSi], [MeHSi], [MeViSi], [Ph₂ Si], [Me₃ Si], and the like.Mixtures of polysilanes may also be employed.

The polysilanes of this invention can be prepared by techniques wellknown in the art. The actual methods used to prepare the polysilanes arenot critical. Suitable polysilanes may be prepared by the reaction oforganohalosilanes with alkali metals as described in Noll, Chemistry andTechnology of Silicones, 347-49 (translated 2d Ger. Ed., Academic Press,1968). More specifically, suitable polysilanes may prepared by thesodium metal reduction of organo-substituted chlorosilanes as describedby West in U.S. Pat. No. 4,260,780 and West et al. in 25 Polym.Preprints 4 (1984), both of which are incorporated by reference.

Preferred polysilanes can be described by the unit formula

    [RSi][R.sub.2 Si]

where there are present 0 to 60 mole percent [R₂ Si] units and 40 to 100mole percent [RSi] units and where each R is independently selected fromthe group consisting of hydrogen, alkyl radicals containing 1 to 20carbon atoms, phenyl radicals, vinyl radicals, and radicals of theformula A_(y) X'.sub.(3-y) Si(CH₂)_(z) -- where A is a hydrogen atom oran alkyl radical containing 1 to 4 carbon atoms, y is an integer equalto 0 to 3, X' is chlorine or bromine, and z is an integer greater thanor equal to 1. Halogen-containing polysilanes of unit formula

    [RSi][R.sub.2 Si],

where there are present 0 to 60 mole percent [R₂ Si] units and 40 to 100mole percent [RSi] units and where the remaining bonds on silicon areattached to other silicon atoms and chlorine atoms or bromine atoms, canbe prepared by the method of Baney et al., U.S. Pat. No. 4,310,651.These halogen-containing polysilanes are generally difficult to handledue to their high reactivity in air. Therefore, polysilanes where thehalogen atoms are replaced with less reactive groups are preferred. Suchless reactive groups include alkyl groups, phenyl groups, amine groups,hydrogen atoms, and Me₃ SiO-- groups. The halogen atoms may be replacedby more than one type of these groups. The halogen atoms may be replacedwith alkyl or phenyl groups by reacting the halogen-containingpolysilanes with alkyl or aryl Grignard reagents or alkyl or aryllithium compounds as described in Baney et al., U.S. Pat. No. 4,298,559.The halogen atoms in the halogen-containing polysilane may also bereplaced with amine groups by reacting the halogen-containing polysilanewith a aminolysis reagent of general formula NHR'.sub. 2 where each R'is independently selected from the group consisting of hydrogen, alkylradicals containing 1 to 4 carbon atoms, and phenyl radicals asdescribed in Baney et al., U.S. Pat. No. 4,314,956; the resultingamino-polysilane contains amino groups of the general formula --NHR'.The halogen atoms may also be replaced by hydrogen atoms by reacting thehalogen-containing polysilane with lithium aluminum hydride as describedin Baney, U.S. Pat. No. 4,310,482. The halogen atoms may also bereplaced with Me₃ SiO-- groups by reacting the halogen-containingpolysilane with Me₃ SiOSiMe₃ as described in Baney, U.S. Pat. No.4,310,481. The just discussed U.S. Pat. Nos. 4,310,651; 4,298,559;4,314,956; 4,310,482; and 4,310,481 are hereby incorporated byreference. These polysilanes are further discussed in Baney et al., 2Organometallics 859 (1983). Still other polysilanes may be used in thepractice of this invention.

The metallic compound must be capable of becoming coordinativelyunsaturated; that is, the metallic compound must be capable ofgenerating or forming open or unoccupied coordination sites. There arethree general methods of generating such sites associated with the metalelement in the metallic compound.

The first method is the alkali metal reduction of the metallic compound.Open coordination sites may be generated from reducible metal compoundsby reaction with alkali metals. By the general term "alkali metal" wemean to include both Group IA alkali metals and Group IIA alkaline earthmetals. Preferred alkali metals include lithium, sodium, potassium, andmagnesium. This method is carried out by combining the polysilane,metallic compound, and the reducing agent at room temperature. Ifdesired, higher or lower temperatures may be used. Suitable reduciblemetallic compounds are of the formula Cp₂ MX₂ where M is titanium,zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum,or tungsten, X is halogen (preferable chlorine), and Cp is acyclopentadienyl group. These cyclopentadienyl compounds are generallycommercially available. The reduction of such complexes are discussed inKool et al., 320 J. Organometallic Chem. 37 (1987) and Sikora et al., 24Inorganic Syntheses 147 (J. Shreeve, ed., Wiley-Interscience, 1986).

The second method of generating open coordination sites is by heating amixture of the polysilane and a metallic compound which containsthermally labile ligands to a temperature less than or equal to about175° C. For polysilanes which contain amine groups, suitable metalliccompounds with thermally labile ligands include organic aluminumcompounds of formula R"₃ Al and organic boron compounds of formula R"₃ Bwhere R" is an alkyl radical containing 1 to 4 carbon atoms. Preferredorganic aluminum and boron compounds are triethyl aluminum and triethylboron.

Other suitable metallic compounds with thermally labile ligands includecompounds of formula (MeCN)₃ M'(CO)₃ where M' is molybdenum or tungsten.Also suitable are alkene and alkyne metal carbonyl compounds where themetal is chromium, molybdenum, or tungsten. Examples of such compoundscan be described by the general formula QM"(CO)₄ where Q iscycloheptatriene, cyclo-octa-1,5-diene, 2,2,1-bicyclohepta-2,5-diene, orsimilar thermally labile groups and M" is chromium, molybdenum, ortungsten. These chromium, molybdenum, or tungsten compounds may be usedwith all polysilanes; amine groups, although they may be present, arenot required.

The third method of generating open coordination sites is by exposure ofa carbonyl-containing metallic compound, in the presence of thepolysilane, to UV irradiation. The metallic compound must contain atleast one carbonyl ligand which can be removed under the influence of UVirradiation. Metallic compounds which contain two or more carbonylligands are preferred. Examples of such suitable carbonyl-containingcompounds include compounds of general formula (C₆ H₆)M"(CO)₃ andcompounds of general formula M"(CO)₆ where M" is chromium, molybdenum,or tungsten. Such carbonyl-containing metallic compounds and theirphotolysis are described in Cotton & Wilkinson, Advanced InorganicChemistry 1049-79 (4th ed., Wiley-Interscience, 1980).

Metallopolysilanes containing two or more metals selected from the groupconsisting of aluminum, boron, chromium, molybdenum, tungsten, titanium,zirconium, hafnium, vanadium, niobium, and tantalum may be also preparedby the methods of this invention. Such mixed metallopolysilanes can beprepared by either the addition of the different metals at the same timeor by sequential addition of the different metals.

The polysilanes and metallic compounds should be reacted in an inert,essentially anhydrous atmosphere. Such reaction conditions help preventexcessive oxygen incorporation into the resulting metallopolysilanes andthe occurrence of possible side reactions. By "essentially anhydrous" wemean that reasonable efforts are made to exclude water from the systemduring the reaction; the absolute exclusion of water is not required.Generally, the inert atmosphere is argon or nitrogen.

Although not wishing to be limited by theory, it is thought that once anopen or coordinatively unsaturated site is generated in the metalliccompound, in the presence of a polysilane, the resulting metalliccomplex is oxidatively added across a Si-Si bond. In other words, thefollowing reactions are thought to occur:

    L.sub.n M→ML.sub.(n-1)

and ##STR1## where M represents the metal atom and L represents theligands. The incorporation of aluminum and boron is thought to occurthrough a different mechanism by reaction of the metallic compound withthe amino group: ##STR2## This reaction may proceed further: ##STR3##Similar reactions may occur for the boron-containing compounds. In anyevent, by the practice of this invention, a metallic-containing group isincorporated into the polysilane.

The metallopolysilanes prepared in this invention generally contain atleast about 0.5 weight percent of the metal. It is generally preferredthat the metal content of the metallopolysilane is between about 2 and10 weight percent; more preferably the metal content is between 4 and 10weight percent. But the metal content, if desired, can be as high as 20to 25 weight percent.

The metallopolysilane of this invention may be pyrolyzed in an inertatmosphere, in a vacuum, or in an ammonia atmosphere at a temperature ofat least 750° C. to give a ceramic material. Pyrolysis under an ammoniaatmosphere should tend to form nitride-containing ceramic materials.Generally, pyrolysis under an inert atmosphere or vacuum is preferred.The polymers may be shaped first (such as an extruded fiber) and thenfired to give a ceramic material. Or the polymers may be filled withceramic type fillers and then fired to obtained filled ceramicmaterials. Additionally, pellets, composites, flakes, powders, and otherarticles may be prepared by pyrolysis of the metallopolysilanes of thisinvention. The ceramic materials produced by the pyrolysis of themetallopolysilanes of this invention generally contain between 2 and 30weight percent of the metal. Preferably the ceramic materials containabout 5 to 10 weight percent of the metal. The metal in the ceramic canbe in the form of a metal carbide and/or a metal silicide; other formsor phases of the metal may also be present. The presence of a metalcarbide or silicide may influence the phase composition of the siliconcarbide in the ceramic material. The presence of the metal in theceramic material may increase the wear resistance of the ceramicmaterial; the metal components may also allow for different electricalor magnetic properties in the ceramic materials.

So that those skilled in the art can better appreciate and understandthe invention, the following examples are given. Unless otherwiseindicated, all percentages are by weight. Throughout the specification"Me" represents a methyl group, "Ph" represents a phenyl group, "Vi"represents a vinyl group, and "Cp" represents a cyclopentadienyl group.In the following examples, the analytical methods used were as follows:

Carbon, hydrogen, and nitrogen were determined on a Control EquipmentCorporation 240-XA Elemental Analyzer. Oxygen analysis was done on aLeco Oxygen Analyzer equipped with an Oxygen Determinator 316 (Model783700) and an Electrode Furnace EF100. Silicon was determined by afusion technique which consisted of converting the silicon material tosoluble forms of silicon and analyzing the solute for total silicon byatomic absorption spectrometry. Metal analyses were carried out byfusing the polymers or ceramic materials with sodium peroxide in aclosed nickel bomb and then dissolving the fusinate in an aqueoussystem. The metal was analyzed by either atomic adsorption spectrometryor inductively coupled plasma-atomic emission spectrometry.

Molecular weights were determined using gel permeation chromatography(GPC) with a Waters GPC equipped with a model 600E systems controller, amodel 490 UV and model 410 Differential Diffractometer detectors; allvalues are relative to polystyrene. IR spectra were recorded on aNicolet 5 DX spectrometer. Pyrolysis was carried out in an Astrographite element tube furnace Model 1000-3060-FP12 equipped with anEurotherm Controller/Programmer Model 822. Powder X-ray analyses wereperformed on a Norelco diffractometer interfaced with a HP 3354computer. Oxidative stability of the ceramic material was evaluated byheating a powdered sample of the ceramic material to 1200° C. for 12hours in air. Thermal stability of the ceramic material was evaluated byfiring a powdered sample of the ceramic material to 1800° C. for 1 hourunder argon.

EXAMPLE 1 POLYMER PREPARATION (A) PREPARATION OF A CHLORINE-CONTAININGMETHYLPOLYSILANE

This polysilane was prepared using the general procedure of U.S. Pat.No. 4,310,651. A mixture of methylchlorodisilanes containing about 48%(Cl₂ MeSi)₂, 40% Cl₂ MeSiSiMe₂ Cl, and 12% (ClMe₂ Si)₂ was placed in athree-neck round bottom flask under an argon purge. The flask wasequipped with a glass inlet tube, overhead stirrer, temperatureprogrammer probe, and a distillation head. About 1.0%tetrabutylphosphonium chloride catalyst from Aldrich Chemical Co. wasadded. The reaction mixture was then heated to 250° C. at 2° C./minwhile byproducts were removed by distillation. The reaction temperaturewas held at 250° C. for about 45 minutes and then cooled to roomtemperature. A pale yellow polymer was obtained in about 15% yield basedon the total weight of the reactants and stored under an inertatmosphere.

(B) PREPARATION OF A CHLORINE-CONTAINING PHENYLMETHYLPOLYSILANE

This polysilane was also prepared using the general procedure of U.S.Pat. No. 4,310,651. A mixture of methylchlorodisilanes (2083.8 g,containing about 48% (Cl₂ MeSi)₂, 40% Cl₂ MeSiSiMe₂ Cl, and 12% (ClMe₂Si)₂) and phenyltrichlorosilane (91.0 g) was reacted as described inExample 1(A), yielding 295.0 g (13.6%) product. This polysilanecontained 40.1% silicon, 29.9% carbon, 0.2% oxygen, and 6.0% hydrogen.

(C) PREPARATION OF A METHYL-CONTAINING METHYLPOLYSILANE

About 25.0 g of the chlorine-containing methylpolysilane of Example 1(A)(containing about 0.15 moles chlorine) was placed, under argon, in athree-neck flask equipped with a gas inlet tube, overhead stirrer, and adistillation head. The polymer was dissolved in about 200 mL toluene,cooled in an ice bath, and then alkylated with methyllithium (0.2 moles)in diethyl ether. The reaction mixture was warmed to room temperatureand then heated to a distillation head temperature of about 100° C.while removing the volatile byproducts. The resulting slurry was cooledin an ice bath and any residual alkylating agent was neutralized withaqueous ammonium chloride. The toluene layer was dried with MgSO₄,filtered, and dried by stripping to 200° C. A white polymer (18.0 g) wasobtained.

(D) PREPARATION OF A METHYL-CONTAINING PHENYLMETHYLPOLYSILANE

The chlorine-containing phenylmethylpolysilane of Example 1(B) (45.0 g,about 0.25 moles chlorine) was methylated with methyllithium (250 mL of1.3M solution in diethyl ether) using a procedure similar to Example1(C). A yellow, resinous solid (20.5 g) was obtained. GPC molecularweight: M_(n) =963, M_(w) =1789; the glass transition temperature was100.4° C.

(E) PREPARATION OF A HYDROGEN-CONTAINING METHYLPOLYSILANE

LiAlH₄ (12.0 g) was placed in a one liter 3-neck flask (equipped with anoverhead stirrer, septa, and argon inlet) under an argon atmosphere.Then 200 mL freshly distilled toluene and 60.0 g of thechlorine-containing polysilane of Example 1(A) in 250 mL toluene wasadded. The resulting slurry was stirred at room temperature for about 15hours. The reaction mixture was cooled in an ice bath at which time anyexcess LiAlH₄ was destroyed by slowly adding 12 mL water, 12 mL of 15%aqueous NaOH, and then 36 mL water. The slurry was filtered and thenstirred over Na₂ SO₄ for about two hours. After a second filtration,toluene was removed by distillation. A hydrogen-containingmethylpolysilane was obtained (25.7 g, 51.4%). The presence of SiH wasconfirmed by IR. GPC molecular weight: M_(n) =1202, M_(w) =2544. Thepolymer contained 47.0% silicon, 20.6% carbon, 2.3% oxygen, 7.4%chlorine, 0.20% nitrogen, and 6.3% hydrogen.

(F) PREPARATION OF A NH₂ -CONTAINING PHENYLMETHYLPOLYSILANE

A chlorine-containing phenylmethylpolysilane similar to that describedin Example 1(B) was dissolved in about 1500 mL toluene and cooled to-78° C. Anhydrous ammonia was rapidly bubbled through the solution forabout two hours. The reaction mixture was warmed to room temperature andthe excess ammonia was allowed to distill off. The solution was filteredand the filtrate concentrated under vacuum. The NH₂ -containingphenylmethylpolysilane was obtained in 12.1% yield.

EXAMPLE 2

The methyl-containing methylpolysilane (10.0 g) of Example 1(C) wasreacted with 5.0 g (0.02 moles) bis(cyclopentadienyl)titanium dichlorideand 2.2 g (0.09 moles) magnesium metal in 200 mL tetrahydrofuran for 20hours at room temperature. The color of the slurry changed from red, togreen, and finally to a dark red-brown. The solvent was removed at 100°C. under vacuum. The gummy solid was extracted with toluene until thetoluene was colorless. The toluene extracts were combined and filtered.The toluene was removed at 150° C., leaving 12.0 g (83.9% yield) of thered-brown polymer containing 36.6% carbon, 7.0% hydrogen, 0.7% oxygen,33.6% silicon, and 4.0% titanium. The glass transition temperature ofthe titanium-containing polymer was 140° C. A sample of thistitanium-containing polysilane was converted to a ceramic material witha char yield of 69.3% by pyrolysis to 1200° C. at 5° C./min and holdingat 1200° C. for two hours under an argon atmosphere. The resultingceramic char contained 36.0% carbon, 44.7% silicon, 0.73% oxygen, and7.3% titanium. The ceramic material had 97.1% mass retention andcontained 24.0% oxygen when evaluated for oxidative stability. Theceramic material had 93.7% mass retention when tested for thermalstability. Quantitative X-ray analysis indicated about 2% alpha-SiC, 58%beta-SiC, and 10% TiC.

EXAMPLE 3

The methyl-containing methylpolysilane (5.0 g) of Example 1(C) and(MeCN)₃ W(CO)₃ (1.0 g) were placed in a 250 mL flask under argon alongwith 100 mL tetrahydrofuran; the polysilane and a portion of the metalcomplex were soluble. The stirred slurry (pale yellow-green) was heatedto 100° C. for 24 hours; a dark black slurry was obtained. After removalof the solvent under vacuum at 100° C., the residue was extracted withtoluene until colorless. The combined extracts were filtered. Afterremoval of the solvent at 150° C., a black polymer was obtained (4.8 g,84.8% yield). The tungsten-containing polymer contained 29.0% carbon,7.2% hydrogen, 4.1% oxygen, 50.6% silicon, and 4.7% tungsten. GPCmolecular weight: M_(n) =1277, M_(w) =3392. An IR spectrum was recordedwith CO-stretching frequencies observed at 1975 (s), 1940 (m), and 1890(w) cm⁻¹. The glass transition temperature of the tungsten-containingpolymer was 60° C. A sample of this tungsten-containing polysilane wasconverted to a ceramic material with a char yield of 66.7% by pyrolysisto 1200° C. at 5° C./min and holding at 1200° C. for two hours under anargon atmosphere. The resulting ceramic char contained 24.2% carbon,47.9% silicon, 5.7% oxygen, and 7.1% tungsten. The ceramic material had103.8% mass retention and contained 10.8% oxygen when evaluated foroxidative stability. The ceramic material had 86.7% mass retention whentested for thermal stability. Quantitative X-ray analysis indicatedabout 50% beta-SiC, 30% WSi₂, and 20% W₅ Si₂.

EXAMPLE 4

The methyl-containing methylpolysilane (2.0 g) of Example 1(C) and(MeCN)₃ W(CO)₃ (4.0 g) were reacted using the same procedure as Example3. A toluene soluble black polymer (2.8 g, 60.3%) was obtained whichcontained 24.2% carbon, 5.3% hydrogen, 12.3% oxygen, 35.6% silicon, and20.9% tungsten. An IR spectrum was recorded with CO-stretchingfrequencies observed at 1962 (s), 1933 (m), and 1868 (vs) cm⁻¹. A sampleof this tungsten-containing polysilane was converted to a ceramicmaterial with a char yield of 61.9% by pyrolysis to 1200° C. at 5°C./min and holding at 1200° C. for two hours under an argon atmosphere.The resulting ceramic char contained 18.8% carbon, 45.0% silicon, 4.7%oxygen, and 26.3% tungsten. The ceramic material had 94.5% massretention and contained 17.7% oxygen when evaluated for oxidativestability. The ceramic material had 91.9% mass retention when tested forthermal stability. Qualitative X-ray analysis indicated the presence ofalpha-SiC, beta-SiC, and WSi₂.

EXAMPLE 5

A 5.0 g sample of the methyl-containing methylpolysilane of Example 1(C)was treated with 1.0 g (MeCN)₃ Mo(CO)₃ in the same manner as in Example3. A black polymer (5.0 g, 89.4%) was obtained which contained 29.1%carbon, 7.4% hydrogen, 3.1% oxygen, 51.5% silicon, and 4.1% molybdenum.An IR spectrum was recorded with CO-stretching frequencies observed at2023 (m), 1883 (s), 1834 (s), and 1784 (m) cm⁻¹. The glass transitiontemperature of the molybdenum-containing polymer was 185° C. A sample ofthis molybdenum-containing polysilane was converted to a ceramicmaterial with a char yield of 66.0% by pyrolysis to 1200° C. at 5°C./min and holding at 1200° C. for two hours under an argon atmosphere.The resulting ceramic char contained 24.8% carbon, 58.1% silicon, 5.1%oxygen, and 6.7% molybdenum. The ceramic material had 103.8% massretention and contained 12.9% oxygen when evaluated for oxidativestability. The ceramic material had 86.9% mass retention when tested forthermal stability. Quantitative X-ray analysis indicated about 10%alpha-SiC, 62% beta-SiC, and 25% MoSi₂.

EXAMPLE 6

The methyl-containing phenylmethylpolysilane (7.0 g) of Example 1(D),molybdenum hexacarbonyl (3.0 g), and 250 mL toluene was placed in a 500mL quartz Schlenk reactor equipped with a reflux condenser. Theresulting clear solution was irradiated with a medium pressure UV lampfor one hour. The irradiation intensity was sufficient to reflux thereaction mixture. The resulting red-black solution was stripped at 100°C. and the residue was extracted with toluene until colorless. Thecombined extracts were filtered. Upon removal of the solvent at 150° C.,7.7 g of a red-black polymer was obtained. The molybdenum-containingpolymer contained 37.9% carbon, 7.6% hydrogen, 2.9% oxygen, 45.1%silicon, and 2.6% molybdenum. GPC molecular weight: M_(n) =705, M_(w)=1083. An IR spectrum was recorded with CO-stretching frequenciesobserved at 1967 (m), 1940 (s), and 1898 (m) cm⁻¹. The glass transitiontemperature of the molybdenum-containing polymer was 129.3° C. A sampleof this molybdenum-containing polysilane was converted to a ceramicmaterial with a char yield of 64.8% by pyrolysis to 1200° C. at 5°C./min and holding at 1200° C. for two hours under an argon atmosphere.The resulting ceramic char contained 31.6% carbon, 53.1% silicon, 5.3%oxygen, and 5.0% molybdenum. The ceramic material had 101.8% massretention and contained 10.7% oxygen when evaluated for oxidativestability. The ceramic material had 86.2% mass retention when tested forthermal stability. Quantitative X-ray analysis indicated about 42%alpha-SiC and 55% beta-SiC.

EXAMPLE 7

A 7.0 g sample of the methyl-containing phenylmethylpolysilane ofExample 1(D) and 3.0 g W(CO)₆ was treated with UV irradiation in thesame manner as in Example 6. A red-black polymer (8.0 g) was obtainedwhich contained 36.5% carbon, 7.2% hydrogen, 4.5% oxygen, 41.0% silicon,and 5.9% tungsten. An IR spectrum was recorded with CO-stretchingfrequencies observed at 1975 (s), 1925 (vs), and 1898 (s) cm⁻¹. Theglass transition temperature of the tungsten-containing polymer was 164°C. A sample of this tungsten-containing polysilane was converted to aceramic material with a char yield of 67.8% by pyrolysis to 1200° C. at5° C./min and holding at 1200° C. for two hours under an argonatmosphere. The resulting ceramic char contained 24.8% carbon, 51.2%silicon, 6.2% oxygen, and 7.1% tungsten. The ceramic material had 102.9%mass retention and contained 13.9% oxygen when evaluated for oxidativestability. The ceramic material had 85.8% mass retention when tested forthermal stability. Quantitative X-ray analysis indicated about 26%alpha-SiC, 50% beta-SiC, and 20% of an unidentified phase.

EXAMPLE 8

The hydrogen-containing methylpolysilane (4.0 g) of Example 1(E) and 1.0g (MeCN)₃ W(CO)₃ were reacted using the same procedure as Example 3except that the mixture was heated to 120° C. for 24 hours. A blackpolymer (4.7 g) was obtained which contained 20.7% carbon, 5.4%hydrogen, 2.3% oxygen, 44.2% silicon, and 5.5% tungsten. An IR spectrumwas recorded with CO-stretching frequencies observed at 2066 (m), 1975(m), 1933 (s), and 1898 (s) cm⁻¹. A sample of this tungsten-containingpolysilane was converted to a ceramic material with a char yield of81.7% by pyrolysis to 1200° C. at 5° C./min and holding at 1200° C. fortwo hours under an argon atmosphere. The resulting ceramic charcontained 23.9% carbon, 57.4% silicon, 6.3% oxygen, and 7.9% tungsten.The ceramic material had 102.4% mass retention and contained 10.8%oxygen when evaluated for oxidative stability. The ceramic material had87.5% mass retention when tested for thermal stability. QualitativeX-ray analysis indicated the presence of beta-SiC, W₅ Si₃, and WSi₂.

EXAMPLE 9

The NH₂ -containing phenylmethylpolysilane (19.3 g) of Example 1(F) wasdissolved in 300 mL of degassed toluene; triethyl aluminum (10.2 g,0.089 moles) was then added with stirring. The reaction mixture wasrefluxed for about two hours and then stirred at room temperature for 60hours. After filtration and concentration of the filtrate under vacuum,15.2 g of a toluene soluble polymer was obtained. This polymer contained38.9% carbon, 8.6% hydrogen, and 30.1% silicon. A sample of thisaluminum-containing polysilane was converted to a ceramic material witha char yield of 66.7% by pyrolysis to 1200° C. at 5° C./min and holdingat 1200° C. for two hours under an argon atmosphere. The resultingceramic char contained 30.7% carbon, 45.7% silicon, and 13.0% aluminum.

EXAMPLE 10

This example is included for comparative purposes only. Atungsten-containing polysilane was prepared from a mixture ofmethylchlorodisilanes, W(CO)₆, and tetrabutylphosphonium chloride usingthe procedure of U.S. Pat. No. 4,762,895. The resultingtungsten-containing polysilane was methylated using methyllithium. An IRspectra of the resulting polysilane exhibited CO-stretching frequenciesat 1919 (vs) and 1869 (s) cm⁻¹. A comparison with the IR spectra of thetungsten-containing polysilane prepared by the method of the presentinvention in Example 7, where the CO-stretching frequencies were 1975(s), 1925 (vs), and 1898 (s) cm⁻¹, shows that the metallopolysilanes ofthe present invention are different from the polysilanes of the priorart. The IR spectra of the tungsten-containing polysilane prepared bythe method of the present invention in Examples 3, 4, and 7 also showthe differences.

That which is claimed is:
 1. A method of preparing a metallopolysilane,which method comprises (A) contacting a polysilane with a metalliccompound capable of generating open coordination sites where themetallic compound contains a metal selected from the group consisting ofaluminum, boron, chromium, molybdenum, tungsten, titanium, zirconium,hafnium, vanadium, niobium, and tantalum and (B) forming opencoordination sites of the metallic compound, in the presence of thepolysilane, until a metallopolysilane is obtained.
 2. A method asdefined in claim 1 wherein the metallopolysilane contains greater than0.5 weight percent of the metal.
 3. A method as defined in claim 2wherein the metallopolysilane contains 2 to 10 weight percent of themetal.
 4. A method as defined in claim 3 wherein the metallopolysilanecontains 4 to 10 weight percent of the metal.
 5. A method as defined inclaim 1 wherein the open coordination sites are generated by reactingthe metallic compound with an alkali metal reducing agent where themetallic compound is reducible.
 6. A method as defined in claim 5wherein the polysilane is described by the unit formula

    [RSi][R.sub.2 Si]

where there are present 0 to 60 mole percent [R₂ Si] units and 40 to 100mole percent [RSi] units and where each R is independently selected fromthe group consisting of hydrogen, alkyl radicals containing 1 to 20carbon atoms, phenyl radicals, vinyl radicals, and radicals of theformula A_(y) X'.sub.(3-y) Si(CH₂)_(z) -- where A is a hydrogen atom oran alkyl radical containing 1 to 4 carbon atoms, y is an integer equalto 0 to 3, X' is chlorine or bromine, and z is an integer greater thanor equal to
 1. 7. A method as defined in claim 5 wherein metalliccompound is described by the formula Cp₂ MX₂ where M is titanium,zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum,or tungsten and X is a halogen.
 8. A method as defined in claim 7wherein X is chlorine.
 9. A method as defined in claim 1 wherein theopen coordination sites are generated by heating the metallic compoundto a temperature less than or equal to about 175° C. where the metalliccompound contains thermally labile ligands.
 10. A method as defined inclaim 9 wherein the polysilane is described by the unit formula

    [RSi][R.sub.2 Si]

where there are present 0 to 60 mole percent [R₂ Si] units and 40 to 100mole percent [RSi] units and where each R is independently selected fromthe group consisting of hydrogen, alkyl radicals containing 1 to 20carbon atoms, phenyl radicals, vinyl radicals, and radicals of theformula A_(y) X'.sub.(3-y) Si(CH₂)_(z) -- where A is a hydrogen atom oran alkyl radical containing 1 to 4 carbon atoms, y is an integer equalto 0 to 3, X' is chlorine or bromine, and z is an integer greater thanor equal to
 1. 11. A method as defined in claim 9 wherein the polysilanecontains amine groups and wherein the metallic compound is described bythe formula R"₃ Al or R"₃ B where R" is an alkyl group containing 1 to 4carbon atoms.
 12. A method as defined in claim 11 wherein R" is an ethylgroup.
 13. A method as defined in claim 9 wherein the metallic compoundis described by the formula (MeCN)₃ M'(CO)₃ where M' is molybdenum ortungsten.
 14. A method as defined in claim 9 wherein the metalliccompound is described by the formula QM"(CO)₄ where Q is selected fromthe group consisting of cycloheptatriene, cyclo-octa-1,5-diene, and2,2,1-bicyclohepta-2,5-diene and where M" is chromium, molybdenum, ortungsten.
 15. A method as defined in claim 1 wherein the opencoordination sites are generated by exposing the metallic compound to UVirradiation where the metallic compound contains at least one carbonylligand.
 16. A method as defined in claim 15 wherein the polysilane isdescribed by the unit formula

    [RSi][R.sub.2 Si]

where there are present 0 to 60 mole percent [R₂ Si] units and 40 to 100mole percent [RSi] units and where each R is independently selected fromthe group consisting of hydrogen, alkyl radicals containing 1 to 20carbon atoms, phenyl radicals, vinyl radicals, and radicals of theformula A_(y) X'.sub.(3-y) Si(CH₂)_(z) -- where A is a hydrogen atom oran alkyl radical containing 1 to 4 carbon atoms, y is an integer equalto 0 to 3, X' is chlorine or bromine, and z is an integer greater thanor equal to
 1. 17. A method as defined in claim 15 wherein the metalliccompound contains two or more carbonyl ligands.
 18. A method as definedin claim 17 wherein the metallic compound is described by the formulaM"(CO)₆ where M" is chromium, molybdenum, or tungsten.
 19. Ametallopolysilane as prepared by method described in claim
 5. 20. Ametallopolysilane as prepared by the method described in claim
 9. 21. Ametallopolysilane as prepared by the method described in claim 15.